Download X - Madison County Schools

AYCI: Do NOT use your
notes.
This fish picture is an example
of codominance. IN YOUR
OWN WORDS, write an
explanation of codominance
based on what you have
learned so far.
RR x WW are parents.
Based on the above picture, do
you think that the flowers
represent codominance as well?
Be prepared to explain your
answer.
AYCI: Using the white boards in your team bucket, on the side of the
room, write the answer to the following questions. Get out your sticker
sheet before I check your work.
1. In snapdragons, heterozygous flowers are pink, while
homozygous flowers are either red or white. When two pink
flowers are crossed, what fraction of the offspring will be pink?
Create a punnett square to answer the question.
A) ¼ or 25%
B) ½ or 50%
C) ¾ or 75%
D) All of them
2. What type of genetic inheritance is described in the above
question?
After I check your answers, erase your white boards, put them in your
bucket, and return them to the side of the room.
1. B) ½ or 50%
R
W
RR
RW
W RW
WW
R
2. Incomplete dominance: this is where two alleles that are
both dominant, do not shadow each other, but create a
phenotype that is blended between the two parent alleles.
Incomplete Dominance,
Codominance, Multiple Alleles,
and Sex-Linked Genes
Fill in the blank notes pg. 1
dominant
blending
RR
heterozygous
Incomplete
alleles
rr
pink
partial
Fill in the blank notes pg. 2
independent
White
both
roan
dominant
Bb
BB
black
Fill in the blank notes pg. 3
co-dominant
blood
I Ai
I BI B
allele
phenotype
3
i
ii
Exit Slip:
• Use scratch paper in the green bucket.
• Turn this into the tray before you leave.
• Write in complete sentences.
Compare and Contrast codominance
with incomplete dominance.
Incomplete dominance
• This is when neither allele is dominant.
• Both alleles are expressed and contribute
equally to the phenotype.
• A heterozygous genotype has an intermediate
phenotype as there is partial influence from both
alleles.
• Example: Red + White = Pink
flower flower flower
Incomplete dominance
• Snapdragons can be
– red (alleles = RR)
– white (alleles = rr)
– pink (alleles = Rr)
• If you cross two pink flowers, is it possible
to produce a white flower?
¼ Red
¼ White
½ Pink
Yes!
Codominance
• Both alleles are dominant.
• They are independent, so there is no
'blending' as in the snapdragons, instead
the phenotype is a result of the full
expression of both alleles.
• Example: black + White = B&W spotted
dog
dog
dog
Codominance
•
•
•
•
•
Dogs can be
Black (alleles = BB)
White (alleles = bb)
Spotted (alleles = Bb)
Is it possible for a black dog to have one
parent that is white?
No!
Multiple alleles (blood typing)
• In the case of the ABO blood grouping,
there are 3 alleles for one gene
• They are written a little differently:
• i : this allele is recessive
• IA : this allele is co-dominant
• IB : this allele is co-dominant
Multiple alleles (blood typing)
•
•
•
•
•
Blood group (phenotype):
A ……………………………..
B ……………………………..
AB ……………………………
O ……………………………..
Possible genotype:
IA IA or IAi
IBIB or IBi
I AI B
ii
Multiple alleles (blood typing)
• A father with homozygous type A blood
has a child with a mother that has
heterozygous type B blood.
• Is it possible for them to have a child with
type O blood?
Sex determination
• Gender is determined by sex
chromosomes in many animals.
• The XY System:
– Female are XX, males are XY
• Y makes the guy!!!
• What are the odds that a couple have a
boy?
50/50
Sex-linked genes
• Some genes are linked to the sex
chromosomes and are inherited with them.
• Hemophilia is carried on the X
chromosome.
• The normal allele is dominant (H)
• The allele for hemophilia is recessive (h)
Sex-linked genes
•
•
•
•
•
XHXH = normal female
XHXh = carrier female
XhXh = female w/hemophilia
XHY = normal male
XhY = male w/hemophilia
A carrier does not
have the disease,
but can pass it on to
their offspring.
Sex-linked genes
• If a female carrier has offspring with a
normal male, what is the chances that
their offspring will have hemophilia?
25%
Sex-linked genes
• In cats the allele for coat color is carried on the X
chromosome.
• The alleles are black and orange but they are
codominant.
• XBXB = black female
• XBY = black male
• XbXb = orange female
• XbY = orange male
• XBXb = tortoiseshell female
Sex-linked genes
• Can an orange male and a black female
produce a tortoiseshell male?
No!
Sex-linked genes
What is the genotype
of the father?
Sex-linked genes
• Mother can provide XB or XO
• Father can provide Y plus 1 other allele.
• Since 1 offspring is XO XO, the father must
provide 1 of these allele.
• Therefore, the father's genotype is XOY